When a well has been drilled and the completion procedure is initiated, one of the important steps is to install tubular members in the well. They are extended past the formation thought to have oil and gas. The oil and gas is produced into the well through perforations which are formed in the tubular member. The perforations are frequently formed by a tubing conveyed perforating assembly, hereinafter referred to as "TCP". The TCP system is lowered into the well on a tubing string. The tubing string is inserted into the well to land the TCP at a specified depth. The designated depth positions the TCP system spanning the formation of interest so that the perforations are formed at the proper depth. The tubing is a small diameter tubing string assembled joint by joint and lowered into the well. After the tubing string has been placed in the well, a weight bar is dropped down the tubing. It travels through the tubing to strike the top of the TCP system to trigger detonation, thereby operating the shaped charges inside the perforating guns. They form perforations into the adjacent formation to enable production.
The weight bar must fall to the bottom of the tubing string to initiate perforation. If it is stalled during the free fall, there is no detonation. The weight bar can be stopped by pipe scale, pipe dope on the inside, drilling fluids in the tubing string, kinks or bends in the tubing string or other reasons. If the weight bar falls partially, but not completely through the tubing string, the stuck weight bar must be retrieved before the TCP is retrieved. Otherwise, there is the risk that the weight bar may be jarred free while retrieving the tubing string and thereby detonate the TCP in the wrong location downhole. This has occurred in times past, namely the perforating guns have been fired at the wrong depth in the well. The perforations were formed at the wrong depth.
To overcome this risk, the present disclosure sets forth a slick line supported device which will be termed a safety anchor. It is run into the tubing string to latch onto the stuck weight bar. The slick line is then retrieved, leaving the safety anchor and weight bar in the tubing held at a locked location. The safety anchor then prevents further fall of the weight bar. The tubing string can then be retrieved from the well without fear that the weight bar will drop, detonating the perforating guns, and forming perforations at the wrong depth in the well.
In summary, the apparatus of the disclosure includes a slick line supported rope socket fitting connected to a setting sub supporting a detachable mandrel. The mandrel is detachable by shearing a shear pin. A fishing neck on the weight bar is clamped by a grapple supported below the mandrel, and radially expandable external slips grip the interior of the tubing string when a shear pin in broken.